The present invention relates to a composition for treating and stabilizing soils, in particular wet soils, comprising, in the form of a powder having a particle size less than 5 mm, quicklime and/or calcium-based hydraulic binders, to the process for preparing such a composition and to the use thereof.
It is known to treat soils, in particular wet soils, in order to dry them and stabilize them, in particular when these soils are intended to serve as foundations for large construction works, such as the construction of roads, car parks, etc. To this end, the soil is mixed with a powdered hydraulic binder or powdered quicklime. These treatments include transferring powdered quicklime or hydraulic binder from the storage reservoir of a spreading vehicle, spreading the powder on the soil to be treated and blending the powder with the soil to be treated, for example by ploughing. In order to achieve suitable transfer conditions, the powder used must be very fluid, i.e. it must have a suitable particle size so that it will flow freely through pipes where transfer is normally made by a pneumatic method. It is moreover appropriate to use a quicklime or binder having a sufficiently fine particle size so as to obtain a dispersion which is as uniform as possible in the soil to be treated and good reactivity. It is usually recommended for example for the foundations of roads, that the quicklime has a particle size which does not exceed 2 mm (see French standard NFP 98-101.
The use of such powders for the treatment of soils has however a certain number of disadvantages, the main one consisting of the emission of lime dust and/or hydraulic binder dust during the treatment described above both during spreading as well as during ploughing. In the presence of wind, it is sometimes possible to observe the transfer of the treatment product by the wind more than 20 to 30 meters from the site area. When this dust is deposited on damp supports or on any unprotected living body, the result is a sudden rise in pH (in the case of lime in particular) or adhesion of the product on these supports following hydraulic setting. The aforementioned dust emissions may thus be aggressive to the environment (corrosion, damage to neighbouring cultivation etc.) and have the effect of leaving visible and tenacious residues on surfaces which it covers, which are unsightly for example in an urban environment (see for example M. SCHAEFFNER and J.-C. VALEUX, Emissions de poussixc3xa8res de chaux et/ou de liants hydrauliques sur les chantiers de traitement de sols et de retraitement de chaussxc3xa9es, rxc3xa9alitxc3xa9 et remxc3xa8des; Bulletin de liaison des laboratoires des Ponts et Chaussxc3xa9es, [Dust emissions from lime and/or hydraulic binders on sites where soils are treated and roadways retreated; reality and remedies; Liaison bulletin of the Highways and Bridges Department], 198, July-August 1995).
Processes are known for stabilizing soils in earthworks or for road foundations comprising spreading a lime wash onto the soil to be treated. This type of treatment is only applicable in the case of dry soils, for example in very sunny regions. It is inapplicable in the case of moderately to very wet soils.
A product is also known for stabilizing soil in civil engineering products, including slaked lime, anhydrous or hydrated gypsum and water or an aqueous solution containing an anti-dust agent (see Derwent abstract of JP-5222366: access number 93-309364). This product uses water or an aqueous solution and, as for the lime wash, it is thus absolutely inappropriate to treat and stabilize soils which are moderately to very wet, as in the case of the present invention.
A surface treatment is also known with quicklime powder, in which the particles of quicklime are coated with an organic compound preferably in solution in an organic solvent. Once these particles are completely coated, the quicklime powder has a distinctly increased resistance to humidity and increased fluidity which improves the conditions of transport and storage (see Japio abstract of JP-58180225). However, when it is necessary to use the powder, it is first necessary to restore its intrinsic reactivity by heating it for ten minutes at approximately 400xc2x0 C. This obviously does not enable it to be considered for the application aimed at by the present invention.
The object of the present invention is to develop a composition for treating and stabilizing soils which meets the requirements of State regulations, while overcoming the disadvantages mentioned above, as well as a process for preparing such a composition and the use thereof.
These problems are resolved by a composition such as indicated at the beginning, additionally including a non-aqueous fluid additive having the power to agglomerate the finer particles of the composition. Advantageously, the composition has a particle size distribution in which the particles smaller than 32 xcexcm represent less than 30% of the total composition, advantageously less than 20% thereof, preferably less than 10% thereof. Also preferably, the composition has a particle size distribution in which the particles larger than 1 mm represent less than 20% of the total composition, advantageously less than 10% and preferably less than 1%.
Quicklime, according to the invention, means lime obtained by firing calciferous materials. A quicklime contains essentially calcium oxide, sometimes with a small magnesium oxide content.
Calcium-based hydraulic binder means cements, for example Portland cement, mixtures of blast furnace slag, fly ash or natural pozzolans and lime, as well as possibly gypsum, sulphocalcic ash etc.
Quicklimes and hydraulic binders for roads usually employed generally have more than 50%, and sometimes even more than 60% of particles smaller than 32 xcexcm. Application to the powdered composition of a non-aqueous additive according to the invention, reduces this fraction of particles smaller than 32 xcexcm by a half and in certain cases by more than 10 times, sometimes by 30 times, while retaining the larger particle size fractions in approximately the same proportions. The result is a distinct reduction in dust emission, without any-adverse influence on the capacity of the product to flow and on its reactivity.
According to one advantageous embodiment of the invention, the said additive is hydrophobic and loses its power of agglomeration when at least part of the quicklime or of the hydraulic binder is hydrated. Consequently, the finer particles are liberated and distributed in the soil to be treated and stabilized in the presence of humidity in the soil, whereas they are no longer in a condition to be dispersed by a side wind. A product can be obtained in this way that is just as effective and acts just as uniformly in the soil as known products currently in use, based exclusively on quicklime or hydraulic binder, without the disadvantages of these latter already mentioned.
According to a particular form of the invention, the said additive can be evaporated at least partially at the temperature of the reaction between quicklime or hydraulic binder and water. As is known, quicklime reacts exothermically with water and hydraulic binders undergo a setting reaction in the presence of water that is also exothermic. After blending the composition according to the invention with a soil, the humidity in the latter reacts with the quicklime or the hydraulic binder, with evolution of heat. This heat may assist in the open air in evaporating the non-aqueous fluid additive which then liberates the finer particles, temporarily agglomerated by it in the stored product.
The additive according to the invention is preferably a compound selected from the group comprising mineral oils and polyolefins-and mixtures thereof. As the mineral oil, the composition according to the invention may include white mineral oil, which is preferably free from or almost free from an aromatic fraction and polynuclear compounds.
Embodiments of the compositions according to the invention are indicated in particular in claims 1 to 14.
The object of the invention is also a process for preparing a composition for treating and stabilizing soils.
According to one embodiment of the invention, this process may comprise grinding a quicklime or a calcium-based hydraulic binder into a finely powdered form, adding the fluid additive to the powder and blending the composition obtained. During this blending, a temporary agglomeration is obtained of the finer particles of the composition by the non-aqueous fluid additive, an agglomeration which will preferably disappear after spreading, in particular by hydration of the quicklime or of the binder which gives rise to a loss of agglomerating power by the additive according to the invention.
According to another embodiment of the invention, the process may also comprise adding the fluid additive to the quicklime or the hydraulic binder and grinding the quicklime or the hydraulic binder into a powder during or after the said addition, with simultaneous blending. This process has the advantage of grinding and blending in a single step.
If, at ambient temperature, the fluid additive is somewhat too viscous, provision can be made to preheat this prior to adding it. It may be considered that the kinematic viscosity of the fluid additive at the moment it is added should preferably not exceed 20 centipoise and even preferably 15 centipoise. Addition at 40xc2x0 C. may for example be considered.
The invention also concerns the use of a composition such as described above for use in the treatment and stabilization of soils, in particular soils that are moderately wet, for example wet clay, loamy or chalky soils. Use will for example be made of such compositions for fill material, road foundations, the retreatment of old roadways, the formation of industrial platforms, the creation of road systems in urban housing estates or in farming areas.